1. Field of the Invention
This invention is directed to wellbore retrieval mechanisms, wellbore packer mills, and to a selective indexing mechanism for wellbore tools.
2. Description of Related Art
The prior art discloses a variety of wellbore packers for installation in the casing of an oil well for isolating upper and lower sections of the casing. A single completion packer has a central bore and surrounding structure that seals the packer inside the casing. Tubing can be connected to or through the packer for withdrawing fluids from the well.
Certain releasable prior art packers release and are readily removable from the casing. Other packers are more or less permanently fixed in the casing. With the readily removable packers corrosion or damage often prevents removal. It is common in oil well operations to mill a packer to remove it from the well. This destroys the packer and milling chips are pumped out of the well or are caught in downhole debris collectors. A magnet removes junk in the well or the junk is milled by a common junk mill. Often the remains of the packer and any tubing or other items hanging from it are freed from the casing and fall free. These things are caught by a grip or catcher on the milling tool and they are moved up and removed from the wellbore.
The remains of the packer often become stuck in the wellbore. The milling tool may become worn or damaged before the packer is free. Thus it may be desirable to remove the milling tool while leaving the remainder of the packer in the well. To do this releasing apparatus is provided on the packer so the mill can then be withdrawn and the well reentered with the same or a different tool for completing removal of the packer.
Known packer mill release apparatuses have slots so the packer mill is releasable by lowering and reversing the direction of rotation. These apparatuses have a multiplicity of moving parts and therefore such mechanisms often jam and the operator must fish the remains of the packer mill as well as the packer, or mill all the junk in the well.
Other prior art apparatuses have pins, screws or stops that shear when a large lifting force is applied to the packer mill so the junk catcher is released and the packer mill can be withdrawn. Use of this apparatus can produce unwanted loose parts such as the ends of pins which require removal from the well. Such loose parts themselves can cause jamming. Deformation of the holes in which such items are inserted may be caused by shear pins and bolts and result in difficulties in reusing the packer mill assembly. This damage may not be readily repaired in the field causing additional delay.
U.S. Pat. No. 4,616,721 discloses a milling tool for removing a packer from a well which includes a releasable catcher for supporting remains of a milled packer. The catcher has a sleeve with deflectable fingers which normally support the remains of the packer. If the packer becomes stuck, the fingers press on a release ring which has a ramp that engages a complementary ramp on a shoulder on the mandrel of the mill. The ramps cam the ring outwardly until the ring breaks in tension at a deliberately weakened location. This releases the sleeve to slide downwardly and permit the fingers to deflect inwardly into a recess thereby clearing the bore of the stuck packer. A retrieval portion of this tool is permanently attached to the milling tool. This retrieval portion must rotate below the packer as the packer is being milled.
U.S. Pat. No. 5,310,001 discloses an apparatus for retrieving downhole devices which includes a retrieving device that can be run on non-conventional work strings such as coiled tubing, wireline, or electric line. The apparatus has a power mandrel, an inner sleeve mandrel slidably disposed within the power mandrel, and an overshot means. Means are provided to translate longitudinal movement of the power mandrel into rotational movement of the inner mandrel. This apparatus does not employ milling to remove a packer and no portion of the equipment may be removed if its latch mechanism is engaged with a packer.
There has long been a need for an efficient and effective packer mill. There has long been a need, recognized by the present inventors, for such a packer mill with a milling device, e.g. a rotary shoe, that can be selectively replaced while leaving other portions of the apparatus, e.g. a spear, in engagement with the packer. The present inventors have also recognized a long felt need for such a packer mill which can be used with a downhole motor or mud motor.